[Show abstract][Hide abstract] ABSTRACT: Congenital muscular dystrophies with hypoglycosylation of α-dystroglycan (α-DG) are a heterogeneous group of disorders often associated with brain and eye defects in addition to muscular dystrophy. Causative variants in 14 genes thought to be involved in the glycosylation of α-DG have been identified thus far. Allelic mutations in these genes might also cause milder limb-girdle muscular dystrophy phenotypes. Using a combination of exome and Sanger sequencing in eight unrelated individuals, we present evidence that mutations in guanosine diphosphate mannose (GDP-mannose) pyrophosphorylase B (GMPPB) can result in muscular dystrophy variants with hypoglycosylated α-DG. GMPPB catalyzes the formation of GDP-mannose from GTP and mannose-1-phosphate. GDP-mannose is required for O-mannosylation of proteins, including α-DG, and it is the substrate of cytosolic mannosyltransferases. We found reduced α-DG glycosylation in the muscle biopsies of affected individuals and in available fibroblasts. Overexpression of wild-type GMPPB in fibroblasts from an affected individual partially restored glycosylation of α-DG. Whereas wild-type GMPPB localized to the cytoplasm, five of the identified missense mutations caused formation of aggregates in the cytoplasm or near membrane protrusions. Additionally, knockdown of the GMPPB ortholog in zebrafish caused structural muscle defects with decreased motility, eye abnormalities, and reduced glycosylation of α-DG. Together, these data indicate that GMPPB mutations are responsible for congenital and limb-girdle muscular dystrophies with hypoglycosylation of α-DG.
The American Journal of Human Genetics 06/2013; · 11.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Congenital muscular dystrophies (CMDs) are early onset disorders of muscle with histological features suggesting a dystrophic process. The congenital muscular dystrophies as a group encompass great clinical and genetic heterogeneity so that achieving an accurate genetic diagnosis has become increasingly challenging, even in the age of next generation sequencing. In this document we review the diagnostic features, differential diagnostic considerations and available diagnostic tools for the various CMD subtypes and provide a systematic guide to the use of these resources for achieving an accurate molecular diagnosis. An International Committee on the Standard of Care for Congenital Muscular Dystrophies composed of experts on various aspects relevant to the CMDs performed a review of the available literature as well as of the unpublished expertise represented by the members of the committee and their contacts. This process was refined by two rounds of online surveys and followed by a three-day meeting at which the conclusions were presented and further refined. The combined consensus summarized in this document allows the physician to recognize the presence of a CMD in a child with weakness based on history, clinical examination, muscle biopsy results, and imaging. It will be helpful in suspecting a specific CMD subtype in order to prioritize testing to arrive at a final genetic diagnosis.
[Show abstract][Hide abstract] ABSTRACT: Glycans are highly diverse carbohydrate moieties that have been selected in evolution to convey dynamic structural and functional properties to the macromolecules to which they are attached. For this reason, correct glycan synthesis is essential for various developmental and physiological processes, particularly in multicellular organisms that use them as communication pathways. The disruption of glycan synthesis frequently results in multisystemic disease with neurological involvement. Congenital disorders of glycosylation (CDGs) have been and will likely remain a rapidly growing group of genetic human diseases that involve different defects in the synthesis or remodelling of N-and O-linked glycans as well as defects in glycosphingolipid and glycosylphosphatidylinositol (GPI) anchor glycosylation. The molecular and clinical characterization of CDGs has enormously contributed to understanding the physiologic roles of the glycosylation machinery and its interaction with other cellular machineries. More than 50 different types of defects have been described and although the first type was described in 1984, CDGs remain widely under-diagnosed or misdiagnosed. This review describes the genetic and biochemical basis of CDGs, as well as the clinical phenotypes and current methods to diagnose them that are ultimately required to establish corrective treatments that are also discussed.
Glycans: Biochemistry, Characterization and Applications, Edited by Mora-Montes H, 05/2012: chapter Congenital Disorders of Glycosylation: pages 59-82; Nova Science., ISBN: 1619425416
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